This application is based on and incorporates herein by reference Japanese Patent Application No. 2001-23256 filed on Jan. 31, 2001 and Japanese Patent Application No. 2001-95932 filed on Mar. 29, 2001.
1. Field of the Invention:
The present invention relates to a valve timing adjusting system of an internal combustion engine capable of staring at an intermediate phase of a camshaft and of a vane rotor, which is generally located in the middle of a variable phase range of the camshaft and of the vane rotor. The valve timing adjusting system can continuously vary opening and closing time phases of each intake valve or each exhaust valve of the internal combustion engine.
2. Description of Related Art:
In one previously proposed variable intake valve timing mechanism, a camshaft is rotated, for example, through a timing pulley and a chain sprocket, which are synchronously rotated with a crankshaft of an internal combustion engine. Opening time and closing time (hereinafter, referred to as xe2x80x9cvalve timingxe2x80x9d) of each intake valve of the internal combustion engine is varied with use of a phase difference produced by relative rotation between the timing pulley or the chain sprocket and the camshaft to increase engine power and to reduce fuel consumption of the internal combustion engine.
By way of example, the fuel consumption can be reduced by reducing pumping losses of the engine. This can be achieved by closing each intake valve after a corresponding piston reaches its bottom dead center. In the case where the intake valve is closed after the piston reaches its bottom dead center, the fuel consumption is advantageously reduced after warming up of the engine, but an actual compression ratio during cold engine operation is disadvantageously reduced, and thus air temperature at a top dead center of the piston cannot be raised to a sufficient level, causing engine start failure. In such a case, the time required to start the engine is increased, or the engine cannot be started.
In the above state, the optimum valve timing of the intake valve during the cold engine operation is on the advanced side relative to the optimum valve timing of the intake valve during the warm engine operation after the warming up. Thus, in the variable intake valve timing mechanism, which changes the valve timing of each intake valve, the optimum valve timing (the optimum opening time and the optimum closing time of each intake valve) suitable for the cold engine start differs from the optimum valve timing (the optimum opening time and the optimum closing time of each intake valve) suitable for reducing the fuel consumption after the warming up of the engine.
To address this disadvantage, there is proposed a variable intake valve timing mechanism (Japanese Unexamined Patent Publication No. 9-324613 corresponding to U.S. Pat. No. 5,738,056), which has a lock pin for locking an internal rotor at an intermediate phase located generally in the middle of a variable phase range of the intake camshaft or of the intake valve timing. With this arrangement, the engine can be started at the intermediate phase which is suitable for the cold engine start.
However, in the above arrangement, lock of the internal rotor generally at the intermediate phase located in the middle of the variable phase range with use of the lock pin at the time of engine stop largely depends on a reduction of oil pressure induced by a reduction in an engine speed. Thus, the reduction of the oil pressure supplied in the advancing chamber varies depending on a change in the temperature of the engine oil. As a result, when the oil pressure supplied to each advancing oil chamber is relatively low at the time of engine stop, the internal rotor and the vanes, which rotate together with the intake camshaft, can not be easily advanced generally to the intermediate phase located in the middle of the variable phase range. Therefore, it is difficult to lock the intake camshaft and the valve timing of the intake valve generally at the intermediate phase located in the middle of the variable phase range.
Japanese Unexamined Patent Publication No. 11-223112 corresponding to U.S. Pat. No. 6,062,182 discloses another variable intake valve timing mechanism, which locks a camshaft and an internal rotor generally at an intermediate phase of a variable phase range of the camshaft and of the internal rotor at the time of engine start with use of a lock pin. This is achieved as follows. At the time of engine stop, the internal rotor and vanes are urged by a spring toward an advance side within an effective range of urging force of the spring, which is between a maximum retarded phase and a maximum advanced phase of the camshaft and of the internal rotor. Then, at the time of engine start, the phase of the internal rotor and of the vanes are fluctuated because of fluctuating torque of the camshaft. This fluctuation of the phase of the internal rotor and of the vanes causes the camshaft and the internal rotor to be locked by the lock pin generally at the intermediate phase of the variable phase range of the camshaft and of the internal rotor.
However, with this arrangement, when the internal rotor and the vanes are stopped at the maximum advance phase at the time of engine stop, the urging force of the spring acts against the retardation of the internal rotor and the vanes caused by the drive torque of the camshaft, so that the internal rotor and the vanes cannot be retarded immediately at the time of engine start, preventing locking of the internal rotor and the vanes by the lock pin. As a result, the engine cannot be reliably started at generally the intermediate phase located in the middle of the variable phase range.
Furthermore, in a case where the valve timing adjusting system is provided to an exhaust camshaft, when both the exhaust camshaft and intake camshaft are in a retarded phase at the time of engine start, an overlap period, during which both the intake valve and the exhaust valve of one cylinder are opened, is unnecessarily increased, causing engine start failure.
Japanese Unexamined Patent Publication No. 11-294121 discloses one technique for solving the above disadvantage. In this technique, one end of a torsion coil spring is engaged with a timing pulley, which is rotated together with a shoe housing, and the other end of the torsion coil spring is engaged with a vane rotor. The vane rotor is always urged in an advance direction relative to the shoe housing by the torsion coil spring.
In the valve timing adjusting system disclosed in the above Japanese Unexamined Patent Publication No. 11-294121, the one end and the other end of the torsion coil spring both axially extend. The other end of the torsion coil spring is inserted and is secured in an axially elongated hole formed in the vane rotor.
When a portion of the torsion coil spring is bent to provide the corresponding axially extending end portion, a curvature R of the bent portion should be equal to or greater than a predetermined value in order to achieve a sufficient strength at the bent portion. The bent portions and the axially extending end portions (engaging portions) of the torsion coil spring increase an axial length of the torsion coil spring, resulting in an increase in an axial size of the valve timing adjusting system.
Furthermore, the other end of the torsion coil spring is inserted in the axially elongated hole formed in the vane rotor, so that the torsion coil spring directly slidably contacts the vane rotor. Thus, the rotor needs to be made from a relatively rigid wear resistant material. However, when the vane rotor is made of the relatively rigid material, a manufacturing cost of the vane rotor is disadvantageously increased, and thus a manufacturing cost of the valve timing adjusting system is disadvantageously increased.
The present invention addresses the above disadvantages. Thus, it is a first objective of the present invention to provide a valve timing adjusting system of an internal combustion engine capable of more reliably advancing a driven-side rotator at least to an intermediate phase of the driven-side rotator located in the middle of a variable phase range of the driven-side rotator with use of hydraulic fluid pressure supplied to each advancing chamber and also with use of urging force of an advance side urging means at the time of engine stop. It is a second objective of the present invention to provide a valve timing adjusting system of the internal combustion engine, which allows the engine to be more reliably started at generally the intermediate phase located in the middle of the variable phase range of the driven-side rotator. It is a third objective of the present invention to reduce an axial size of a valve timing adjusting system by reducing an axial length of a torsion coil spring. It is a fourth objective of the present invention to reduce a cost of a valve timing adjusting system by reducing a manufacturing cost of a vane rotor by forming the vane rotor with a relatively soft material. It is a fifth objective of the present invention to reduce the cost of a valve timing adjusting system by reducing a manufacturing cost required for engaging a torsion coil spring to a vane rotor through use of a positioning hole, which is formed in the vane rotor and to which the torsion coil spring is engaged.
To achieve the objectives of the present invention, there is provided a valve timing adjusting system of an internal combustion engine for adjusting opening time and closing time of at least one of intake and exhaust valves. The valve timing adjusting system is provided in a driving force transmission system that allows the internal combustion engine to be started at generally an intermediate phase of a driven shaft located in the middle of a variable phase range of the driven shaft, which is driven by a driving shaft of the internal combustion engine to open and close the at least one of the intake and exhaust valves. The valve timing adjusting system includes a driving-side rotator, driven-side rotator, an advancing chamber, a retarding chamber, a hydraulic pressure supply/drain means, a phase restraining means and an advance side urging means. The driving-side rotator is rotated synchronously with the driving shaft of the internal combustion engine. The driven-side rotator is rotated together with the driven shaft and is capable of relative rotation relative to the driving-side rotator. The advancing chamber applies hydraulic fluid pressure to the driven-side rotator to rotate the driven-side rotator in such a manner that a phase of the driven-side rotator is advanced relative to the driving-side rotator. The retarding chamber applies hydraulic fluid pressure to the driven-side rotator to rotate the driven-side rotator in such a manner that the phase of the driven-side rotator is retarded relative to the driving-side rotator. The hydraulic pressure supply/drain means supplies the hydraulic pressure to the advancing chamber and drains the hydraulic pressure from the retarding chamber when the internal combustion engine is turned off. The phase restraining means restrains the relative rotation between the driving-side rotator and the driven-side rotator at generally an intermediate phase of the driven-side rotator after the engine is turned off or when the engine is started. The intermediate phase of the driven-side rotator is located in the middle of a variable phase range of the driven-side rotator. The advance side urging means applies urging force to the driven-side rotator to advance the;driven-side rotator on an advance side. An effective range of the urging force of the advance side urging means is between a maximum retarded phase of the driven-side rotator and a predetermined phase of the driven-side rotator. The predetermined phase of the driven-side rotator is located near an intermediate phase of the driven-side rotator on an advance side of the intermediate phase of the driven-side rotator.
The advance side urging means can be a spring. One end of the spring can be retained by the driving-side rotator, and the other end of the spring can be retained by the driven-side rotator and extends in a direction perpendicular to an axial direction of the driven-side rotator. The driven-side rotator can include an engaging portion for engaging with the other end of the spring. The engaging portion can extend in the direction perpendicular to the axial direction of the driven-side rotator.
The engaging portion of the driven-side rotator can receive a wear resistant member made of a wear resistant material. The wear resistant member is arranged between the other end of the spring and the engaging portion of the driven-side rotator.
The driven-side rotator can include a positioning hole, which axially penetrates through the driven-side rotator for positioning the driven-side rotator to the driven shaft. The other end of the spring retained by the driven-side rotator can be alternatively extended in the axial direction of the driven-side rotator and can be engaged with the positioning hole.